One thing that's unfortunate is that you can't guarantee that what's shown online on itn (which is behind many of the booking engines: their own, trip.com, United, ANA, etc, etc) is actually real.

A friend of mine tried booking a trip the other day with all segments showing availability, yet it failed in the final booking stage. It turned out that the flight that was booked out was showing Y4 on itn! She phoned a travel agent and waitlisted for it.

So, depending on where you are looking up the information, it may mean sweet FA.